A principal theoretical problem in understanding wall turbulence is the determination of how turbulence is created and sustained, i.e., the explanation of how energy is transferred from the mean flow to the turbulence. Flow-oriented vortical eddies have been associated with large Reynolds stresses and with the production of turbulence in the viscous region close to the wall. Their creation and evolution are investigated in a high-resolution direct numerical simulation of turbulent flow in a channel. An important finding is that they regenerate themselves by a process that appears to be weakly dependent on the outer flow. This involves the enhancement of streamwise vorticity at the wall, of opposite sign, at a location where a stress-producing eddy lifts from the wall.

The mechanism for the deposition of spherical aerosols on a wall is investigated in a high resolution direct numerical simulation of low Reynolds number turbulent flow in a vertical channel. A Stokes drag force is used in the equation of motion for the aerosol and the particles are assumed to have no influence on the flow field. A particle deposits when it is one radius from the wall. This occurs mainly by an inertial-free flight from distances outside the viscous sublayer. Particle concentration profiles are presented as a function of time and as a function of distance from the channel walls. It is shown that particles accumulate in the viscous sublayer by turbophoresis and by free flights that do not carry particles to the wall. A new method for identifying free-flight particles is presented and a prediction of free-flight deposition is made using fluid velocity distributions.

The trajectories of aerosols are computed in a high-resolution direct numerical simulation of turbulent flow in a vertical channel. The aerosol equation of motion includes only a Stokes drag force and the influence of the aerosols on the gas flow is assumed to be negligible. Since the flow is vertical, aerosols deposit as a consequence of the turbulent fluctuations and their own inertia. It is shown that the eddies which are responsible for aerosol deposition are the same eddies that control turbulence production. Typical aerosol trajectories are shown and related to eddy structure. A free-flight theory suggested by Friedlander and Johnstone [Ind. Eng. Chem. 49, 1151 (1957)] is found to be based on reasonable assumptions about typical velocities of depositing aerosols as they pass through the viscous sublayer, but the theory is shown to be deficient in other respects. The distribution of normal velocities of the aerosols that deposit is compared to the distribution of fluid particle velocities in the viscous sublayer and some support is found for the notion that the probability distribution of Eulerian velocities may be useful in predicting deposition.